Electric circuit and sensor for detecting arcing and a transparency having the circuit and sensor

ABSTRACT

An electrical system responsive to overheating and/or electric arcing of an electrically conductive member, e.g. a heating member of an aircraft windshield, includes a first switch in a first current path, and a second switch in a second current path. The first current path is from an electrical power supply through the first switch, through an arc sensor to the heating member to the power supply. The second current path is from a temperature sensor monitoring the temperature of the heating member through the second switch to a temperature controller. When the temperature of the heating member is at or above a predetermined value, the temperature controller causes the first switch to open. When there is arcing, the second switch is moved to the open position. The temperature controller senses that the second switch is open and causes the first switch to open.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject matter of this application is related to the subject matterof U.S. patent application Ser. No. 12/345,932 filed on Dec. 30, 2008 inthe names of Ali N. Rashid, Monroe A. Stone and James R. Priddy, Jr.titled “A METHOD OF AND SYSTEM FOR MAINTAINING OPERATING PERFORMANCE OFA TRANSPARENCY, and U.S. patent application Ser. No. 12/345,952 filed onDec. 30, 2008 in the names of All Rashid, Monroe A. Stone and JamesPriddy and titled TRANSPARENCY HAVING SENSORS. U.S. patent applicationSer. Nos. 12/345,932 and 12/345,952 in their entirety are herebyincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electric circuit and sensor for detectingarcing and a transparency having the sensor, and more particularly, toan electric circuit and sensor for detecting arcing of an electricalheating system of an aircraft transparency, e.g. a laminated aircraftwindshield and to a laminated aircraft windshield having portions of theelectric circuit and sensor.

2. Discussion of the Available Technology

Aircraft or aerospace windows, e.g. aircraft windshields include alaminate of plastic layers or sheets, glass layers or sheets andcombinations thereof. The layers of an inner segment of the windshieldface the interior of the aircraft and provide structural stability tothe windshield. The layers of an outer segment of the windshield facethe exterior of the aircraft. The outer segment of the windshield, whichcan also provide structural stability, is usually provided withaccessories for visual acuity. For example and not limiting to thediscussion, the outer segment of the windshield can include anelectrical conductive coating, or a plurality of electrical conductivewires, between and connected to a pair of spaced bus bars to heat theouter surface of the windshield to prevent the formation of fog, snowand ice, and/or to remove fog, snow and ice from, the surface of thewindshield facing the exterior of the aircraft, also referred to as theouter surface of the windshield.

As is appreciated by those skilled in the art, as the service oroperating time of the aircraft windshield increases, the operatingefficiency of the windshield decreases until such time that theaccessories of the windshield become non-functional, and the windshieldneeds to be replaced or repaired. More particularly and not limiting tothe discussion, the peripheral edge of the windshield has an outboardmoisture seal that is a barrier to prevent moisture from enteringbetween the plastic and glass layers or sheets of the windshield. Whenthe seal fails, e.g. cracks and/or the layers de-bond due to erosioncaused by wind and rain; moisture enters between the layers of thewindshield. While the cracking or de-bonding of the seal is not astructural issue, when moisture moves between the layers of thewindshield, the windshield can de-laminate, and the conductive coatingor wires, whichever is present, can be damaged and fail, therebyreducing the service life of the windshield. More particularly, whendelamination of the windshield occurs, increased amounts of moisturemove between the layers of the windshield accelerating the degradationof the windshield, e.g. causing arcing, damage and/or failure of the busbars and the electrical conductive coating or wires thereby reducing oreliminating the defrosting capabilities of the windshield.

At the present time sensors for detecting arcing are available, e.g.disclosed in the above-mentioned U.S. patent application Ser. Nos.12/345,932 and 12/345,952. Although the presently available sensors fordetecting arcing are acceptable, they have limitations. For example, butnot limiting to the discussion, the presently available sensors fordetecting arcing of an electrical conductive coating between two busbars measures the current at a first bus bar and the current at apredetermined position on the conductive coating or at the second busbar. When the difference between the two measurements exceeds apredetermined current difference, a signal is forwarded to a controlsystem to discontinue the current input to the bus bars. This type ofsensor does not take into account that the current to the bus barsincludes electric noise and interference that results from the airplanegenerator providing electrical power to the aircraft transparency, thelights, the air conditioner and other electrical equipment of theaircraft. As a result, the readings are not an accurate representationof current variations caused by arcing.

Based on the preceding discussion, it can be appreciated by thoseskilled in the art that it would be advantageous to provide an electriccircuit and sensor for detecting arcing, and a transparency havingcomponents of the circuit and sensor, that eliminates the limitations ofthe presently available electric circuits and sensors for detectingarcing.

SUMMARY OF THE INVENTION

This invention relates to an electrical system responsive to overheatingand/or electric arcing of an electrically conductive member. The systemincluding, among other things, a temperature sensor for sensing thetemperature of the electrically conductive member; a first switch to beelectrically connected to a power source; an arc sensor for monitoringvoltage of the electrically conductive member, the arc sensorelectrically connected to the first switch, wherein the first switch ina closed position provides a continuous electrical path through thefirst switch to the arc sensor, and the first switch in the openposition prevents current from moving through the first switch; atemperature controller acting on the first switch to selectively openthe first switch; a second switch electrically connecting thetemperature sensor to the temperature controller, wherein the firstswitch in a closed position electrically interconnects the temperaturesensor and the temperature controller, and in an open positiondisconnects the first switch and the temperature sensor; a filter andmodifying system connected to the arc sensor and acting on the secondswitch, wherein with the first switch and the second switch in theclosed position a first electric path is provided through the firstswitch to the electrically conductive member and a second electricallyconductive path is provided from the temperature sensor, through thesecond switch, to the temperature controller, wherein the temperaturecontroller opens the first switch when the temperature controllerreceives a predetermined signal from the temperature sensor, and whereinthe filter and modifying system opens the second switch when a signalfrom the arc sensor indicates a predetermined level of arcing, and thetemperature controller responsive to the opening of the second switchopens the first switch, if the first switch is closed.

Further, this invention relates to an aircraft including, among otherthings, a windshield, including, among other things, a heatable memberfor removing snow, fog or ice from an outer surface of the windshield,the heatable member comprising a pair of spaced bus bars and anelectrically conductive member between and in electrical contact withthe spaced bus bars, and an electrical system to monitor and/or controlperformance of the heatable member. The electrical system including,among other things, a temperature sensor for sensing the temperature ofthe electrically conductive member; a first switch to be electricallyconnected to a power source of the aircraft; an arc sensor formonitoring voltage of the electrically conductive member, the arc sensorelectrically connected to the first switch, wherein the first switch ina closed position provides a continuous electrical path from the powersource of the aircraft through the first switch to the arc sensor andfrom the arc sensor to a first one of the pair of spaced bus bars of theheatable member, and the second one of the spaced bus bars of theheatable member connected to the power source, and the first switch inthe open position prevents current from moving from the power source tothe first bus bar; a temperature controller acting on the first switchto selectively open the first switch; a second switch electricallyconnecting the temperature sensor to the temperature controller, whereinthe first switch in a closed position electrically interconnects thetemperature sensor and the temperature controller, and in an openposition disconnects the first switch and the temperature sensor; afilter and modifying system connected to the arc sensor and acting onthe second switch, wherein with the first switch and the second switchin the closed position a first electric path is provided from the powersupply through the first switch, through the heatable member to thepower source, and a second electrically conductive path is provided fromthe temperature sensor, through the second switch, to the temperaturecontroller, wherein the temperature controller opens the first switchwhen the temperature controller receives a predetermined signal from thetemperature sensor, and wherein the filter and modifying system opensthe second switch when a signal from the arc sensor indicates apredetermined level of arcing, and the temperature controller responsiveto the opening of the second switch opens the first switch, if the firstswitch is closed.

Still further, this invention relates to a method of controllingelectrical input to a heatable member of an aircraft transparency toeliminate overheating and/or arcing, wherein the heatable membercomprises an electrically conductive member to heat outer surface of thetransparency. The method includes, among other things forwarding asignal representing a temperature of the electrically conductive memberthrough a first switch, through a temperature controller to a secondswitch, wherein when the temperature controller indicates a temperatureequal to or above a predetermined value, the temperature controller actsto open the second switch; monitoring current/voltage from a powersource to the electrically conductive member as the current/voltageflows from the power source through the second switch to theelectrically conductive member, wherein the monitoring is at a positionbetween the second switch and the electrically conductive member andprovides monitoring information, and acting on the monitoringinformation to open the first switch when the monitoring information haspredetermined selected information, wherein opening the first switchopens the second switch.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an isometric view of an aircraft having non-limitingembodiments of the invention.

FIG. 2 is an isometric view of an aircraft transparency incorporatingfeatures of the invention.

FIG. 3 is a view taken along lines 3-3 of FIG. 2.

FIG. 4 is an isometric view of a heatable member of an aircrafttransparency having a block diagram to indicate features of theinvention to detect arcing of the heatable member.

FIG. 5 is a block diagram of a non-limiting embodiment of an intelligentelectrical power controller and monitoring system of the inventionconnecting an electrical power supply of the aircraft to the heatablemember of the type shown in FIG. 4.

FIG. 6 is a block diagram of a non-limiting embodiment of an arcmonitoring system of the invention.

FIG. 7 is an elevated front view of a cabinet housing a healthmonitoring system for the aircraft, the health monitoring systemincorporating features of the invention to detect arcing of the heatablemember of the type shown in FIG. 4.

FIG. 8 is a partial cross sectional view of an aircraft transparency ofthe type shown in FIG. 3 having selected components of the electriccircuit and sensor of the arc detector of the invention mounted on thetransparency in accordance with the teachings of the invention.

FIG. 9 is a fragmented elevated plan view of another non-limitingembodiment of the invention for mounted selected components of theelectric circuit and sensor of the arc detector of the invention on anaircraft window of the type shown in FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, spatial or directional terms such as “inner”, “outer”,“left”, “right”, “up”, “down”, “horizontal”, “vertical”, and the like,relate to the invention as it is shown in the drawing on the figures.However, it is to be understood that the invention can assume variousalternative orientations and, accordingly, such terms are not to beconsidered as limiting. Further, all numbers expressing dimensions,physical characteristics, and so forth, used in the specification andclaims are to be understood as being modified in all instances by theterm “about”. Accordingly, unless indicated to the contrary, thenumerical values set forth in the following specification and claims canvary depending upon the property desired and/or sought to be obtained bythe present invention. At the very least, and not as an attempt to limitthe application of the doctrine of equivalents to the scope of theclaims, each numerical parameter should at least be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques. Moreover, all ranges disclosed herein are to beunderstood to encompass any and all subranges subsumed therein. Forexample, a stated range of “1 to 10” should be considered to include anyand all subranges between and inclusive of the minimum value of 1 andthe maximum value of 10; that is, all subranges beginning with a minimumvalue of 1 or more and ending with a maximum value of 10 or less, e.g.,1 to 6.7, or 3.2 to 8.1, or 5.5 to 10. Also, as used herein, the term“positioned over” or “mounted over” means positioned on or mounted overbut not necessarily in surface contact with. For example, one article orcomponent of an article “mounted over’ or positioned over” anotherarticle or component of an article does not preclude the presence ofmaterials between the articles, or between components of the article,respectively.

Before discussing several non-limiting embodiments of the invention, itis understood that the invention is not limited in its application tothe details of the particular non-limiting embodiments shown anddiscussed herein since the invention is capable of other embodiments.Further, the terminology used herein to discuss the invention is for thepurpose of description and is not of limitation. Still further, unlessindicated otherwise, in the following discussion like numbers refer tolike elements.

Non-limiting embodiments of the invention will be directed to aircraftlaminated transparencies, and in particular, to an aircraft windshield.The invention, however, is not limited to any particular type ofaircraft and aircraft transparency, and the invention can be practicedon any type of aircraft and aircraft transparency, e.g. but not limitedto windows of the type having a medium responsive to electric stimuli toincrease or decrease visible transmission, e.g. but not limited to thetype of window disclosed in U.S. Published Patent Application2007/0002422A1, and on aircraft windows of the type having an insulatedair space between a pair of laminated sheets. The entire disclosures ofthe publications identified in this paragraph are hereby incorporated byreference.

Further, the invention can be practiced on commercial and residentialwindows, e.g. but not limited to the type disclosed in U.S. Pat. No.5,675,944, which patent in its entirety is hereby incorporated byreference; a window for any type of land vehicle; an aircraft canopy,cabin window and windshield for any type of air and space vehicle, awindow for any above or below water vessel, and a window for a viewingside or door for any type of containers, for example but not limited toa refrigerator, cabinet and/or oven door. Still further, the inventionis not limited to the material of the layers or sheets of the aircraftwindow, and the layers or sheets can be made of, but not limited to,cured and uncured plastic sheets; annealed, heat strengthened, and heatand chemically strengthened, clear, colored, coated and uncoated glasssheets. Still further the invention can be practiced on windows havingopaque sheets, e.g. but not limited to wood and metal sheets, and glasssheets having an opaque coating, and combinations thereof.

Shown in FIG. 1 is an aircraft 18 having a non-limiting embodiment of anaircraft windshield 20 (FIGS. 2-4), and arc sensor and monitor (seeFIGS. 5-9) of the invention. The windshield 20 (FIG. 3) includes a firsttransparent sheet 22 secured to a second transparent sheet 24 by a firstvinyl-interlayer 26; the second sheet 24 secured to a secondvinyl-interlayer 28 by a first urethane interlayer 30, and the secondvinyl-interlayer 28 secured to a heatable member 32 by a second urethaneinterlayer 34. An edge member or moisture barrier 36 of the type used inthe art, e.g. but not limited to a silicone rubber or other flexibledurable moisture resistant material is secured to (1) peripheral edge 38of the windshield 20, i.e. the peripheral edge 38 of the first andsecond sheets 22, 24; of the first and second vinyl-interlayers 26, 28,and the first and second urethane interlayers 30, 34 and of the heatablemember 32; (2) margins or marginal edges 40 of outer surface 42 of thewindshield 20, i.e. the margins 40 of the outer surface 42 of the firstglass sheet 22 of the windshield 20, and (3) margins or marginal edges44 of outer surface 46 of the windshield 20, i.e. margins of the outersurface 46 of the heatable member 32.

As is appreciated by those skilled in the art and not limiting to theinvention, the first and second glass sheets 22, 24; the first andsecond vinyl-interlayers 26, 28 and the first urethane interlayer 30form the structural part, or inner segment, of the windshield 20, andthe outer surface 42 of the glass sheet 22 of the windshield 20 facesthe interior of the aircraft 18 (hereinafter the outer surface 42 of theglass sheet 22 is also referred to as the inner surface 42 of thewindshield 20), and the second urethane layer 34 and the heatable member32 form the non-structural part, or outer segment, of the windshield 20,and the surface 46 of the heatable member 32 of the windshield 20 facesthe exterior of the aircraft 16. The heatable member 32 provides heat toprevent fog from forming on, to remove fog from, to prevent snow and icefrom forming on, and/or to melt snow and ice on, the outer surface 46 ofthe heatable member 32 of the windshield 20 (hereinafter the outersurface 46 of the heatable member 32 is also referred to as the outersurface 46 of the windshield 20) in a manner discussed below.

As can be appreciated, the invention is not limited to the constructionof the windshield 20 and any construction of aircraft transparencies,e.g. aircraft windshields used in the art can be used in the practice ofthe invention. For example and not limiting to the invention, thewindshield 20 can include a construction wherein the vinyl interlayer 28and the urethane interlayer 30 are omitted, and/or the sheets 22 and 24are glass or plastic sheets. Generally the sheets 22 and 24 of thewindshield 20 are clear chemically strengthened glass sheets; however,the invention is not limited thereto, and the glass sheets 22 and 24 canbe heat strengthened or heat tempered glass sheets. Further as isappreciated by those skilled in the art, the invention is not limited tothe number of glass sheets, vinyl interlayers or urethane interlayersthat make up the windshield 20, and the windshield 20 can have anynumber of sheets and/or interlayers.

The invention is not limited to the design and/or construction of theheatable member 32, and any electrical conductive heatable member usedin the art to heat a surface of a sheet to prevent the formation of fog,snow and/or ice on, to melt snow and ice on, and/or to remove fog, snowand ice from, the outer surface of a windshield can be used in thepractice of the invention. With reference to FIG. 4, in one non-limitingembodiment of the invention, the heatable member 32 includes the glasssheet 60 having a conductive coating 62 applied to surface 64 of theglass sheet 60, and a pair of spaced bus bars 66, 68 in electricalcontact with the conductive coating 62. The invention is not limited tothe composition of the conductive coating 62, and any of the electricalconductive coatings known in the art can be used in the practice of theinvention. For example and not limiting to the invention, the conductivecoating 62 can be made from any suitable electrical conductive material.Non-limiting embodiments of conductive coatings that can be used in thepractice of the invention include, but are not limited to, a pyrolyticdeposited fluorine doped tin oxide film of the type sold by PPGIndustries, Inc. under the trademark NESA®; a magnetron sputterdeposited tin doped indium oxide film of the type sold by PPGIndustries, Inc under the trademark NESATRON®; a coating made up of oneor more magnetron sputter deposited films, the films including, but notlimited to a metal film, e.g. silver between metal oxide films, e.g.zinc oxide and/or zinc stannate, each of which can be appliedsequentially by magnetron sputtering, e.g. as disclosed in, but notlimited to, U.S. Pat. Nos. 4,610,771; 4,806,220 and 5,821,001. Thedisclosures of U.S. Pat. Nos. 4,610,771; 4,806,220 and 5,821,001 intheir entirety are hereby incorporated by reference.

As can be appreciated, the invention is not limited to the use of anelectrical conductive coating to heat the glass sheet 60, and theinvention contemplates the use of any type of member that can beelectrically heated, e.g. but not limited to electrical conductingwires. The wires, e.g. wires 69 shown in phantom in FIGS. 3 and 4 can beembedded in a sheet of a plastic interlayer, e.g. but not limited to theinterlayer 34 between the bus bars 66 and 68, and electrically connectedto the bus bars 66 and 68. Such a heating arrangement is known in theart under the PPG Industries Ohio Inc. trademark AIRCON® and isdisclosed in U.S. Pat. No. 4,078,107, which patent in its entirety isincorporated herein by reference.

The invention is not limited to the design and/or construction of thebus bars 66 and 68, and any of the types of bus bars used in the art canbe used in the practice of the invention. Examples of bus bars that canbe used in the practice of the invention, include, but are not limitedto, the types disclosed in U.S. Pat. Nos. 3,762,902; 4,623,389;4,894,513; 4,994,650, and 4,902875, which patents in their entirety arehereby incorporated by reference.

With continued reference to FIG. 4, in one non-limiting embodiment ofthe invention, each of the bus bars 66 and 68 are connected by a wire 70and 71, respectively, to an intelligent electrical power controller andmonitoring system 72 of the invention (discussed in more detail below),and the controller and monitoring system 72 is connected to aircraftelectrical power supply 74 by wires or electric cables 76 and 77.Although not limiting to the invention, ends 79 of the bus bar 66, andends 80 of the bus bar 68 are spaced from adjacent sides 82-85 of theglass sheet 60, and sides 86 of the coating 62 are spaced from the sides82-85 of the glass sheet 60, to prevent arcing of the bus bars 66 and68, and the coating 62 with metal body cover 87 of the aircraft 18 (seeFIG. 1).

A temperature sensor 88 is mounted on the conductive coating 62 to sensethe temperature of the conductive coating 62 of the heatable member 32,and is connected to the intelligent electrical power controller andmonitoring system 72 by a wire or electric cable 92 in a mannerdiscussed below. The invention is not limited to the temperature sensor88, and any of the types used in the art can be used in the practice ofthe invention. Further, the invention is not limited to the number oftemperature sensors 88 mounted on the coating 62, and any number, e.g.one, two or three can be mounted on the coating 62 to sense thetemperature of different areas of the coating 62. In one non-limitingembodiment of the invention, the temperature sensor was a thermocouple,and three thermocouples were mounted on the coating 62.

With reference to FIG. 5, in one non-limiting embodiment of theinvention, the aircraft power supply 74 supplies alternating electriccurrent along the wires 76 and 77 to a window heat controller 93 of theintelligent electrical power controller and monitoring system 72. As isappreciated by those skilled in the art, the invention is not limited tothe power supply 74 and the power supply 74 can be an alternatingcurrent supply as shown in FIG. 5 or a direct current supply as is knownin the art. The wire 76 is connected to one pole of a switch 98 of thewindow heat controller 93, and the other pole of the switch 98 isconnected to an arc sensor 99 of an arc monitoring and detecting system100 of the invention by a wire or electric cable 102. The switch 98 isusually in the closed position and is moved from the closed position tothe open position and vise versa by signals forwarded along wire orelectric cable 104 from a control logic for a heat controller 106 of thewindow heat control 93. The arc sensor 99 is connected to the bus bar 66of the heatable member 32 by the wire 70. The bus bar 68 of the heatablemember 32 is connected to the power supply 74 by the wire 71.

In one non-limiting embodiment of the invention, components of theintelligent electrical power controller and monitoring system 72 aremounted in a Faraday box 109, and the Faraday box 109 connected toground, e.g. the body 81 of the aircraft 18 (see FIG. 1) by the wire orcable 111 (see FIG. 5) to block out external static electric fields.

With continued reference to FIG. 5, the temperature sensor 88 isconnected to one pole of an electronic switch 110 by the wire 92, and asecond pole of the switch 110 is connected by wire 112 to the controllogic 106 of the window heat controller 93. The switch 110 is usually inthe closed position and is moved from the closed position to the openposition and from the open position to the closed position by signalsforwarded to the switch 110 along wire or electric cable 114 from asignal filtering and modifying system 116 of the arc monitoring anddetecting system 100.

The arc monitoring and detecting system 100 of the invention providesfor electrically disconnecting the heating member 32 and the powersupply 74 from one another when any of the following conditions aredetected; (a) the temperature of the heatable member 32 is greater thana predetermined temperature, (b) major arcing, and (c) there is a seriesof micro-arcing greater than an allocated predetermined number in agiven time period.

Consider now Condition (a) the temperature of the heatable member 32 isgreater than a predetermined temperature. With reference to FIG. 5, theswitch 98 of the window controller 93 and the switch 110 are each in theclosed position to heat the heatable member 32 to remove fog, snowand/or ice snow from the outer surface 46 of the windshield 20 (see FIG.3). The temperature of the heatable member 32 is sensed by thetemperature sensor 88 and the signal of the temperature sensor 88, e.g.in millivolts (“mV”) is monitored by the heat controller 106 of thewindow heat controller 93. When the temperature of the heatable member32 exceeds a given temperature, e.g. but not limiting to the discussionbecause of arcing or an increase in the resistance of the coating 62,the heat controller 106 forwards a signal to the switch 98 along thewire 104 to open the switch 98 to electrically disconnect the powersupply 74 and the heatable member 32 from one another. The invention isnot limited to the cause of the heatable member 32 exceeding thepredetermined temperature and any type of defect of the heatable member32 that caused the predetermined temperature to be exceed is included inthe practice of the invention.

The discussion is now directed to a non-limiting embodiment of thesignal monitoring and detecting system 100 of the invention. The signalmonitoring and detecting system 100 of the invention is designed todetect and act on two different levels of arcing, namely Conditions (b)and (c). One level of arcing (Condition (b)) is termed “major-arcing”and is defined as measured voltage/current exceeding a firstpredetermined level. The value of the first predetermined level is notlimiting to the invention, and the value is selected such that arcing isvisible with the unaided eye and/or based on prior experience can damagethe window 20. In one non-limiting embodiment of the invention, thefirst predetermined level is based on the model of the window and thecurrent needed to heat the window to remove fog, snow and ice, and forprevent the formation of fog, snow and ice, on the surface of thewindow. For example and not limiting to the invention, a window for aGulfstream aircraft, model number G650, is expected to need 18 21.6amperes to remove fog, snow and ice, and/or prevent the formation offog, snow and ice, on the surface of the window. Through observation ofthe performance of the window when heated, the first predetermined levelfor this window model for Condition (b) is equal to or above 150millivolts (“mV”).

Consider now the case when there is major arcing without the temperatureexceeding the predetermined temperature. The arc sensor 99 senses themajor arcing and forwards a signal to the signal modifying system 116.The signal modifying system 116 forwards a signal along the wire 114 toopen the switch 110. The control logic of heat controller 106 determinesthat the switch 110 is in the open position and sends a signal along thewire 104 to open the switch 98 to electrically disconnect the powersupply 74 and the heatable member 32 from one another. As can beappreciated by those skilled in the art, when there is major-arcing andthe temperature of the heatable member 28 exceeds the predeterminedtemperature, the switch 110 and/or the switch 98 can open.

Another level of arcing (Condition (c)) is termed “micro-arcing” and isdefined as the measured voltage/current exceeding a second predeterminedvalue and less than the first predetermined value. In one embodiment ofthe invention, the value of the second predetermined level is selectedsuch that the noise level in the current moving through the arc sensingsystem 99 is filtered out. For example and not limiting to theinvention, the noise level for the electrical system of the Gulfstreamaircraft was determined for purposes of this invention to be 50 mV, e.g.the voltage measured along cable 102/70 (FIG. 5). Based on the abovediscussion, in one non-limiting embodiment of the invention,micro-arcing occurs in the range of equal to or greater than 50 mV andless than 150 mV, and major-arcing occurs in the range of equal to orgreater than 150 mV, the voltage measured along the wire 70.

In general, a single micro-arc does not adversely effect the operationof the heatable member 32, however, it has been determined that a seriesof micro-arcs in a given time period is usually followed by majorarcing. Therefore, monitoring micro-arcing can be used to prevent majorarcing and prevent damage to the window. The predetermined number ofmicro-arcs in a given time period can be determined from observation andhistory. In another non-limiting embodiment of the invention, thepredetermined number of micro-arcs can be assigned based on astatistical analysis of the performance of heatable members 32. In thepractice of the invention, for the Gulfstream aircraft under discussion,the predetermined number for a given time period, e.g. 10 seconds, was256.

Consider now the case where there is a series of micro-arcing greaterthan a predetermined number in a given time period without a temperatureincrease, and/or an indication that there is major arcing. The signalmodifying system 116 counts the number of micro-arcs in a given timeperiod in a manner discussed below and when the number of micro-arcingfor the given time period is greater than the predetermined number, thesignal modifying system 116 forwards a signal along the wire 114 to openthe switch 110. The control logic of the heat controller 106 determinesthat the switch 110 is in the open position and sends a signal along thewire 104 to open the switch 98 to electrically disconnect the powersupply 74 and the heatable member 32 from one another. As can beappreciated by those skilled in the art, when there is excessivemicro-arcing and the temperature of the heatable member 28 exceeds thepredetermined temperature, the switch 110 and/or the switch 98 can open.

Arcing of interest in the present discussion includes, but is notlimited to, electric arcing over a crack in the coating 62 and/or one orboth bus bars 66 and 68, and/or separation of the bus bars 66, 68 and/orthe coating 62. As is appreciated by those skilled in the art, impactsto the glass sheet 60 of the heatable member 32 can result in fracturesin the glass sheet 60 that result in fractures in the coating 62.Further, moisture moving through the moisture barrier 36 of thewindshield 20 (see FIGS. 2 and 3) can cause delamination of thelaminated windshield. Delamination of the windshield can result inseparation of one or both of the bus bars 66 and 68 from the conductivecoating 62, or the wires embedded in the interlayer 38. The electricarcing over cracks in the conductive coating 62 and separations betweenthe bus bars and the coating result in spot heating which can reachtemperatures to cause the glass 60 of the heatable member 32 tofracture. The invention is not limited to the cause of the electricarcing, and arcing resulting from any type of defect of the heatablemember 32 is included in the practice of the invention.

The discussion is now directed to a non-limiting embodiment of the arcmonitoring and detection system 100 of the invention. The arc monitoringand detection system 100 of the invention is designed to detectmajor-arcing and micro-arcing, and take action to prevent or limitdamage to the heatable member 32 and/or the window 20. The switch 98 andthe switch 110 (see FIG. 5) are of the type that open and close inresponse to signals forwarded to the switch. In the practice of theinvention, the switch 98 was of an electronic solid state switch. Thecontrol logic of the heat controller 106 of the window heat controller93 was a comparator of the type that compares the electrical signal,e.g. in mV from the temperature sensor 88 to a set voltage range, andwhen the signal is outside of the range, the control logic of the heatcontroller 106 forwards a signal to open the switch 98, and when thesignal is within the range, the control logic of the heat controller 106sends a signal along the wire 104 to close the switch 98.

Another feature of the invention is that the control logic of the heatcontroller 106 can open and close the switch 98 when there is nomajor-arcing and/or the number of micro-arcs is less than apredetermined number for a given time period. More particularly, whenthere is major-arcing and/or the number of micro-arcs is greater than apredetermined number for a given time period, the signal filtering andmodifying system 116 of the arc monitoring and detecting system 100forwards a signal along the wire 114 to maintain switch 110 in the openposition, which maintains the switch 98 in the open as previouslydiscussed. The switches 110 and 98 remain open until the arcing problemis resolved. After the arcing problem is solved, the switch 110 isclosed. The switch 110 can be closed manually, or by a signal fromfiltering and modifying system 116 because there no longer ismajor-arcing, or micro-arcing greater than the predetermined number forthe given time period.

With reference to FIG. 6, the discussion is now directed to the arcdetecting and monitoring system 100 to detect major and micro-arcing,and take action to prevent or minimize damage to the heatable member 32and/or the window 20 (see FIGS. 3 and 4). As shown in FIG. 6, the arcdetector 99 is connected to the wire 102 and 70, and the output of thearc detector 99 passed onto the filter 148 by the wires 150. Theinvention is not limited to the type of arc detector 99 used in thepractice of the invention. In the preferred practice of the invention,the arc detector 99 used was a current transformer to reduced thecurrent to a lower level for ease of filtering the current moving alongthe wires 102 and 70. More particularly, the current transformer 99produces a reduced current accurately proportional to the currentpassing through the wires 102/70 to the heatable member 32. For example,in one non-limiting embodiment of the invention, the current passingthrough the heatable member 32 was 185 amperes and the output of thecurrent transformer 99 was 1.85 amperes. As can be appreciated by thoseskilled in the art, a reduction from 185 amperes to 1.85 amperesrequires the use of a current transformer that has a core (not shown)capable of such a reduction without deterioration of the core due to theheat generated during the reduction. In one non-limiting embodiment ofthe invention, the current transformer 99 used was sold by Metglas andmade of Metglas material. Further as can be appreciated by those skilledin the art, the invention is not limited to the amount of currentreduction, and current reduction in the ranges of 25-95% and 50-90% iscontemplated by the invention. Still further as can be appreciated bythose skilled in the art, the invention is not limited to the use of acurrent transformer as the arc sensor and the invention contemplates theuse of a shunt resistor and a measured resistor as an arc sensor in thepractice of the invention.

With continued reference to FIG. 6, the signal filter 148 of the signalfiltering and modifying system 116 is a high pass filter to effectivelyeliminate electrical and magnetic noises from the signals passing alongthe wires 150. The filter level of the signal filter 148 is based onnoise spectral analysis of the electrical system, i.e. the currentpassing from the power supply 74 to the heatable member 32. As discussedabove, in one non-limiting embodiment of the invention signals below 50mV were filtered out of the signal. The filter 148 also reduces themagnitude of the line signal due to elimination of the high frequencycomponent, e.g. but not limiting to the invention by 2 levels.

The signal from the signal filter 148 is passed onto a two stage filter154. The first stage 154A includes a comparator to filter out signalshaving voltage/current levels above the first predetermined level, e.g.150 mV indicating major arcing. When the signal of the first stageexceeds the first predetermined level, a signal is sent along the line156 to the signal switch 140 that major arcing has been detected, andthe signal switch 140 sends a signal along the line 114 to open theswitch 110, which causes the control logic of the heat controller 106 toopen the switch 98 to prevent the current from moving from the powersupply 74 to the heatable member 32 (see FIG. 5) as discussed above.

The signal from the first stage 154A of the filter is passed onto thesecond stage 154 b. The signal having a voltage/current value within therange of the first and the second predetermined levels, e.g. between 50to 150 mV are indicative of micro-arcing. The second stage 154 b of thetwo stage filter 154 counts the number of impulses in the signal betweenthe first and the second predetermined levels for a given time period,which is indicative of micro-arcing for the give time period. In onenon-limiting embodiment of the invention when the count exceeds 256 fora time period of 10 seconds, excess micro-arcing is considered to haveoccurred, and the filter 154B forwards a signal along the line 156 tothe signal switch 140 that excessive micro-arcing has been detected. Thesignal switch 140 sends a signal along the line 114 to open the switch110, which causes the control logic of the heat controller 106 to openthe switch 98 to prevent the current from moving from the power supply74 to the heatable member 32 (see FIG. 5) as discussed above. In theinstance when the time period ends and the count of micro-arcing is lessthan the predetermined number, the filter 154B restarts the count foranother time period.

With continued reference to FIG. 6, the signal filter 148 and the dualfilter 154 are each connected by a wire 158 and 160, respectively, to amicro-computer 164, and the micro-computer 164 is connected toelectronic storage 166 by wire or cable 168. The micro-computer 164 setsthe level, e.g. the second predetermined level for the filter 148 tofilter the noise from the signal from the arc detector 99, sets thelevel, e.g. the first predetermined level for the filter 154A toidentify major-arcing, and sets the count and time period for the filter154B for the micro-arc count. The electronic storage 166 maintains ahistory of the activities of the filter 148 and two stage filter 154 toprovide data for setting the predetermined first level indicatingmicro-arcing, the second predetermined level indicating noise level inthe signal from the arc detector 99, and the micro arc count and timeperiod to indicated a potential problem due to micro-arcing.

In one non-limiting embodiment of the invention, the micro-computer 164contains the “firmware” which is a burnt in program right on electronicboard. The system software was a Windows® based application program. Thesystem is able to detect the two different levels of arcing, e.g.major-arcing and micro-arcing that can be set by the user. Once amicro-arc is detected a counter is enabled in order to keep track of howmany micro-arcs occur in a defined period of time. These events arestamped with date, time and magnitude of the arc and then stored on acircuit board for later retrieval.

The signal filtering and modifying system 116 provides three orders ofdiscrimination. A very low discrimination order, e.g. 50 mV, which isassociated with unwanted external noise, if any, is the first order tobe adjusted. Under this order, the signals are disregarded as beingcaused by noise from the power supply 72. The second order are signalsabove a first predetermined level indicating major-arcing. And the thirdorder are signals between the first predetermined level and the secondpredetermined level indicating micro-arcing.

Although not limiting to the invention, data process for micro-arcingwas as follows: if the computer 164 finds a flip-flop high in a closesuccession without any break, then the computer 164 handles this bunchof data as a pocket. The experience is that spark impulses come ingroups, which will be represented by the packets. One packet can includea maximum number of impulses, e.g. but not limiting to the invention 256impulses. The term “impulse” does not mean the impulses, e.g. the MHzimpulses are above the output of the filter 154B, but it means that thecomputer 164 found a packet on the output of the bistable multi-vibratorcommonly called flip flop in the time measuring cycle, e.g. 10 millesecond long. In one non-limiting embodiment of the invention, when thenumber of impulses exceeds a set amount, e.g. 256 within the given timeperiod, e.g. 10 seconds, then the 256 impulse will constitute a newpacket for a new time period. First experiments, in general showed thatthe packets are roughly 1-40 impulses long.

With reference to FIG. 7, in another non-limiting embodiment of theinvention, the computer 164 and electronic storage 166 are mounted in acabinet 210 housing the health monitoring system of the airplane 18. Inone non-limiting embodiment of the invention, the cabinet 210 caninclude a speaker 212 connected to the signal switch 140 by a wire oroptical coupler 213 (see FIG. 6) to provide audible informationregarding the performance of the heatable member 32 of the windshield20, and an alarm 214 to bring attention to the computer 164 to providethe personnel within the aircraft with real time performance of thewindshield 20. In another non-limiting embodiment of the invention, thecabinet 210 has a wireless transmitter and receiver 220 to transmitsignals 222 regarding the performance of the heatable member 28 (seeFIG. 4) of the windshield 20 and to receive signals 224 regardingscheduled times and locations when repair and maintenance of thewindshield 20 is required, as disclosed in U.S. patent application Ser.No. 12/345,932.

In another non-limiting embodiment of the invention, the Faraday box 109having selected ones of the components of the intelligent electricalpower controller and monitoring system control system 72 (see FIG. 5) ismounted to the peripheral edge of the window 20 (see FIG. 8). In thisnon-limiting embodiment of the invention, the Faraday box 109 is mountedover the peripheral edge 38 of the windshield 20, e.g. but not limitingto the invention over the peripheral edges of the glass sheets 22 and 24and the interlayer 26. A protective plastic layer 230 is providedbetween the peripheral edge 38 of the windshield 20 and the Faraday box109 to prevent marring of the glass edges due to vibrations. A cable 232extends out of the edge sealing member 36 and is connected to cable 234by connector 236 of the type used in the aircraft art. In thisembodiment of the invention, the components mounted in the Faraday Box109 include, but are not limited to, the filter 148, the dual filter 154and the signal switch 140. The cables 232 and 234 carry the wires 70 and71 to the heatable member 32, the wire 114 from the signal switch 140 tothe switch 110, and the wire 150 from the arc detector 99 and the wires158 and 160 from the computer 164 to the filter 148 and the two stagefilter 154. The wire 111 connects the Faraday Box 109 to ground (seeFIG. 5). The edge sealing member 38 overlays the marginal edges 40 andthe peripheral edges 38 of the windshield 20 as discussed above, and theedge sealing member 38 also overlays the Faraday Box 109 as shown inFIG. 8. After the windshield 20 is mounted in the body of the aircraft18, the cables 222 and 224 are connected.

With reference to FIG. 9, there is shown another non-limiting embodimentof the invention for mounting the intelligent electrical powercontroller and monitoring system 72 (see FIG. 5) of the invention to thewindshield. In FIG. 9, the glass sheet 22 has an integrated circuit 260including, but not limiting to the invention, the filter 148, the twostage filter 154 and the signal switch 140 applied over the surface 262of the glass sheet 22 opposite to the surface 42 of the glass sheet 22facing the interior of the aircraft 18. The interlayer 26 overlays thesurface 262 of the glass sheet 22 as discussed above and overlays theintegrated circuit 260. Applying integrated circuits to a glass surfaceis well known in the art and no further discussion is deemed necessary.

The invention is not limited to the embodiments of the inventionpresented and discussed above which are presented for illustrationpurposes only, and the scope of the invention is only limited by thescope of the following claims and any additional claims that are addedto applications having direct or indirect linage to this application.

What is claimed is:
 1. An electrical system responsive to overheatingand/or electric arcing of an electrically conductive member, the systemcomprising: a temperature sensor for sensing the temperature of theelectrically conductive member; a first switch to be electricallyconnected to a power source; an arc sensor for monitoring voltage of theelectrically conductive member, the arc sensor electrically connected tothe first switch, wherein the first switch in a closed position providesa continuous electrical path through the first switch to the arc sensor,and the first switch in the open position prevents current from movingthrough the first switch; a temperature controller acting on the firstswitch to selectively open the first switch; a second switchelectrically connecting the temperature sensor to the temperaturecontroller, wherein the first switch in a closed position electricallyinterconnects the temperature sensor and the temperature controller, andin an open position disconnects the first switch and the temperaturesensor; a filter and modifying system connected to the arc sensor andacting on the second switch, wherein with the first switch and thesecond switch in the closed position a first electric path is providedthrough the first switch to the electrically conductive member and asecond electrically conductive path is provided from the temperaturesensor, through the second switch, to the temperature controller,wherein the temperature controller opens the first switch when thetemperature controller receives a predetermined signal from thetemperature sensor, and wherein the filter and modifying system opensthe second switch when a signal from the arc sensor indicates apredetermined level of arcing, and the temperature controller responsiveto the opening of the second switch opens the first switch, if the firstswitch is closed.
 2. The electrical system according to claim 1, whereinthe arc sensor is a current transformer and the current transformerproduces a reduced current proportional to the current passing throughthe current transformer.
 3. The electrical system according to claim 2,wherein the current transformer has a core made of Metglas material. 4.The electrical system according to claim 1 wherein the electricallyconductive member is a heating member having a pair of spaced bus barswith an electrically conductive coating between and electricallyconnected to the bus bars, wherein the arc sensor is electricallyconnected to one of the bus bars, and the other bus bar is electricallyconnected to an electric power source, and the first switch iselectrically connected to the power source.
 5. The electrical systemaccording to claim 4 wherein the heating member is a layer of anaircraft laminated transparency.
 6. The electrical system according toclaim 5 wherein the arc sensor and the filter and modifying system aremounted in a Faraday box.
 7. The electrical system according to claim 6,wherein the Faraday box is mounted on the aircraft laminatedtransparency.
 8. The electrical system according to claim 5, wherein thefilter and modifying system is in the form of a printed circuit andadhered to a surface of one of a layer of the aircraft laminatedtransparency.
 9. The electrical system according to claim 5, wherein theaircraft transparency is an aircraft windshield.
 10. The electricalsystem according to claim 1, wherein the predetermined signal receivedby the temperature controller from the temperature sensor indicates thatthe electrically conductive member is equal to or has exceeded apredetermined temperature.
 11. The electrical system according to claim1, wherein the signal from the arc sensor to the filter and modifyingsystem above a current/voltage first predetermined level indicates majorarcing, which is arcing at the electrically conductive member that isvisible with the unaided eye, the filter and modifying system filtersthe signal from the arc sensor below a current/voltage secondpredetermined level to filter out electric noise, wherein thecurrent/voltage above the second predetermined level and below the firstpredetermined level is defined as minor arcing.
 12. The electricalsystem according to claim 11, wherein the filter and modifying systemforwards a signal to the second switch to open the second switch whenthe current/voltage is equal to or above the second predetermined level,and forwards a signal to the second switch to open the second switchwhen the current/voltage is equal to or above the second predeterminedlevel and below the first predetermined level.
 13. The electrical systemaccording to claim 12, wherein a signal to open the second switch issent by the filter and modifying system when there is a predeterminednumber of micro arcing within a predetermined time period.
 14. Theelectrical system according to claim 13, wherein the predeterminedsignal received by the temperature controller from the temperaturesensor indicates that the electrically conductive member is equal to orhas exceeded a predetermined temperature.
 15. An aircraft comprising awindshield, comprising a heatable member for removing snow, fog or icefrom an outer surface of the windshield, the heatable member comprisinga pair of spaced bus bars and an electrically conductive member betweenand in electrical contact with the spaced bus bars, and an electricalsystem to monitor and/or control performance of the heatable member, theelectrical system comprising: a temperature sensor for sensing thetemperature of the electrically conductive member; a first switch to beelectrically connected to a power source of the aircraft; an arc sensorfor monitoring voltage of the electrically conductive member, the arcsensor electrically connected to the first switch, wherein the firstswitch in a closed position provides a continuous electrical path fromthe power source of the aircraft through the first switch to the arcsensor and from the arc sensor to a first one of the pair of spaced busbars of the heatable member, and the second one of the spaced bus barsof the heatable member connected to the power source, and the firstswitch in the open position prevents current from moving from the powersource to the first bus bar; a temperature controller acting on thefirst switch to selectively open the first switch; a second switchelectrically connecting the temperature sensor to the temperaturecontroller, wherein the first switch in a closed position electricallyinterconnects the temperature sensor and the temperature controller, andin an open position disconnects the first switch and the temperaturesensor; a filter and modifying system connected to the arc sensor andacting on the second switch, wherein with the first switch and thesecond switch in the closed position a first electric path is providedfrom the power supply through the first switch, through the heatablemember to the power source, and a second electrically conductive path isprovided from the temperature sensor, through the second switch, to thetemperature controller, wherein the temperature controller opens thefirst switch when the temperature controller receives a predeterminedsignal from the temperature sensor, and wherein the filter and modifyingsystem opens the second switch when a signal from the arc sensorindicates a predetermined level of arcing, and the temperaturecontroller responsive to the opening of the second switch opens thefirst switch, if the first switch is closed.
 16. The aircraft accordingto claim 15, wherein the arc sensor is a current transformer and thecurrent transformer produces a reduced current proportional to thecurrent passing through the current transformer.
 17. The aircraftaccording to claim 15 wherein the arc sensor and the filter andmodifying system are mounted in a Faraday box.
 18. The aircraftaccording to claim 17, wherein the Faraday box is mounted on theaircraft transparency.
 19. The aircraft according to claim 15, whereinthe filter and modifying system is in the form of a printed circuit andadhered to a surface of one of a layer of the aircraft laminatedtransparency.
 20. The aircraft according to claim 15, wherein thepredetermined signal received by the temperature controller from thetemperature sensor indicates that the electrically conductive member isequal to or has exceeded a predetermined temperature.
 21. The aircraftaccording to claim 15, wherein the signal from the arc sensor to thefilter and modifying system above a current/voltage first predeterminedlevel indicates major arcing, which is arcing at the electricallyconductive member that is visible with the unaided eye, the filter andmodifying system filters the signal from the arc sensor below acurrent/voltage second predetermined level to filter out electric noise,wherein the current/voltage above the second predetermined level andbelow the first predetermined level is defined as minor arcing andcomprising a controller acting on the filter and modifying system tochange settings of the filter and modifying system.
 22. The aircraftaccording to claim 21, wherein the filter and modifying system forwardsa signal to the second switch to open the second switch when thecurrent/voltage is equal to or above the second predetermined level, andforwards a signal to the second switch to open the second switch whenthe current/voltage is equal to or above the second predetermined leveland below the first predetermined level.
 23. The aircraft according toclaim 22, wherein a signal to open the second switch is sent by thefilter and modifying system when there is a predetermined number ofmicro arcing within a predetermined time period.
 24. The aircraftaccording to claim 23, wherein the predetermined signal received by thetemperature controller from the temperature sensor indicates that theelectrically conductive member is equal to or has exceeded apredetermined temperature.
 25. A method of controlling electrical inputto a heatable member of an aircraft transparency to eliminateoverheating and/or arcing, wherein the heatable member comprises anelectrically conductive member to heat outer surface of thetransparency, the method comprising: forwarding a signal representing atemperature of the electrically conductive member through a firstswitch, through a temperature controller to a second switch, whereinwhen the temperature controller indicates a temperature equal to orabove a predetermined value, the temperature controller acts to open thesecond switch; monitoring current/voltage from a power source to theelectrically conductive member as the current/voltage flows from thepower source through the second switch to the electrically conductivemember, wherein the monitoring is at a position between the secondswitch and the electrically conductive member and provides monitoringinformation; acting on the monitoring information to open the firstswitch when the monitoring information has predetermined selectedinformation, wherein opening the first switch opens the second switch.26. The method according to claim 25 wherein the predetermined selectedinformation indicates arcing of the electrically conductive member.